The long-term goal of this project is to determine the influence of host genetic and environmental factors on clinical, radiographic, and microbiological measures of periodontal disease through the study of twins. Periodontal disease affects three-fourths of American adults, and it is estimated that five to six billion dollars per year is required to treat existing disease. Although clinical and bacterial risk factors have been well-studied, the influence that host genetic factors have on this disease is largely undetermined. In years 01-03, we established a Minnesota Periodontal Twin Registry which includes 175 pairs of adult monozygous and dizygous twins reared together and apart. Clinical periodontal measures, dental radiographs, and subgingival plaque samples were obtained from all consenting subjects. Analyses to date indicate that a significant portion of the population variance for clinical and radiographic measures of disease are attributable to genetic variance. The specific aims of this current proposal are to: 1) recruit and evaluate 36 additional pairs of older (equal to or greater than 50 years of age) reared-together twins to increase our sample of twins with moderate to severe periodontal disease; 2) evaluate 24 additional pairs of reared-apart twins; 3) assay archived and subsequently obtained plaque samples from 235 pairs of twins using monoclonal antibodies specific against five putative periodontal microbial pathogens; and 4) determine the influence of genetic, early family environmental, and unshared environmental factors on the clinical, radiographic, and microbiological measures of periodontal disease. Volunteers will be recruited through the Minnesota Center for Twin and Adoption Research. Each twin will be independently evaluated by two calibrated examiners who will be blinded to the subject's zygosity. Clinical measures of disease will be recorded and subgingival plaque samples obtained from six index teeth and in one randomly selected quadrant. Both univariate and multivariate data analyses will be completed, and several twin models will be tested to determine the most appropriate model of the genetic and environmental components of phenotypic variance. Determining the influence of genetic factors in periodontal disease may lead to the development of early and aggressive preventive strategies for those individuals most at risk for developing disease or acquiring pathogenic oral microorganisms.